writing in a pre-existing txt file ?

Question

Mahmoud Khadijeh 2020-1-14

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/500250-writing-in-a-pre-existing-txt-file

评论： Mahmoud Khadijeh 2021-5-25

采纳的回答： Walter Roberson

Hello,

I have a question regarding writing my outputs to a pre-existing text file in a specific line

example :

in the text file I have the following :

A =

B =

I want my code to write the results next to A and B in the text file

The results will be ( for example ):

A = 1 2 3 4 5 6

B = 4 5 6 7 8 9

Can we do that in MATLAB ?

Thanks,

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Walter Roberson 2020-1-15

Note that it is not possible in any operating system MATLAB is supported on, to append text to a line, except by rewriting everything from that point to the end of file. Only the IBM MVS version of MATLAB (we are talking decades ago!) could put text on the end of a line, and only for files initialized a particular way; the mechanism involved each line being fixed length. DEC's VMS is the only operating system that MATLAB was ever been supported on that really supported inserting variable amounts of text to the end of a line without rewriting to end of file and without the lines being fixed length -- but for technical reasons, MATLAB never supported that particular kind of VMS file.

In all file systems and operating systems after the two I mention above, files are represented as streams of bytes, and the only way to add to a line is to copy the entire rest of file .

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Answer 1

Walter Roberson 2021-5-24

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https://ww2.mathworks.cn/matlabcentral/answers/500250-writing-in-a-pre-existing-txt-file#answer_707338

在 MATLAB Online 中打开

S = fileread('YourFile.txt');
parts = regexp(S, '\r?\n', 'split');
if isempty(parts{end}); parts(end) = []; end   %trailing newline
parts{1} = [parts{1} ' 1 2 3 4 5'];
parts{2} = [parts{2} ' 4 5 6 7 8'];
fid = fopen('NewFile.txt', 'wt');
fprintf('%s\n', parts{:});
fclose(fid);

It is not recommended that you write to the same file that is your input: if there were a problem in processing then you might have corrupted the original file.

As I discussed in January, it is not possible in any supported operating system to insert text at the end of a line without reading the entire rest of the file and rewriting it. All file systems on all systems supported by MATLAB are only streams of bytes that have no possible way to insert in place.

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Walter Roberson 2021-5-24

在 MATLAB Online 中打开

Sorry,

fprintf('%s\n', parts{:});

should have been

fprintf(fid, '%s\n', parts{:});

Mahmoud Khadijeh 2021-5-25

Thank You sir!

it works.

Regards,

Mahmoud

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Answer 2

Akira Agata 2020-1-15

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https://ww2.mathworks.cn/matlabcentral/answers/500250-writing-in-a-pre-existing-txt-file#answer_410189

在 MATLAB Online 中打开

Assuming the pre-existing text file is data.txt, how about the following?

cInput = readcell('data.txt','Delimiter','\n');
cAppend = {'1 2 3 4 5 6';'4 5 6 7 8 9'};
cOutput = strcat(cInput,cAppend);
writecell(cOutput,'data.txt')